The correct answer is B) Class B. The blanketing effect is essential for Class B fires, which involve flammable liquids and gases. Blanketing these types of fires with a smothering agent like foam or carbon dioxide cuts off the oxygen supply and effectively extinguishes the fire. In contrast, Class A fires (ordinary combustibles), Class C fires (energized electrical equipment), and Class D fires (combustible metals) require different extinguishing techniques that do not rely primarily on the blanketing effect.